A network in compliance with the IEEE 1394 standard provides asynchronous communication of a best effort type, and isochronous communication which ensures a transmission bandwidth and a cyclic transfer. However, a network system in compliance with the IEEE 1394 standard is not configured so as to monitor the operating states of the nodes on the IEEE 1394 compliant network.
Japanese Patent Application Publication No. 2001-308951-A describes a packet transmission and reception processing unit that is suitable for an asynchronous connection. In the packet transmission and reception processing unit, if a packet processing controller circuit on a consumer's side has failed to process a received packet within a predetermined period of time, a packet processing control timer detects a time-out and informs a CPU of the time-out. In response, the CPU issues packet processing suspend instruction and packet transmit instruction for the controller circuit via a register. The controller circuit suspends the current packet processing and produces header and data for a write response (WRS) packet, which is transmitted to a producer node via a bus. In this manner, a packet can be processed without causing a time-out at the producer node.
Japanese Patent Application Publication No. 2002-135262-A describes a network monitoring system. In the network monitoring system, a control means updates the value of a time information area in a corresponding MAC address of a table for each arrival of a packet. Upon reception of a monitoring command for a network interface card (NIC), the control means refers to the time information area of the table, without conducting packet transfer to the NIC. When a difference between the value of the time information area and current time is within a predetermined time, the control means in response informs a monitoring device of the normal operation of the NIC. When the difference exceeds the predetermined time, the control means informs the device of the occurrence of abnormality in the NIC or a line to the NIC.
Japanese Patent Application Publication No. 2003-8579-A describes a cyclic data communication system. In the cyclic data communication system, a communication node assigned to a management station periodically transmits a cyclic trigger packet indicative of the start of a communication cycle in the isochronous communication phase. In response to the cyclic trigger packet sent from the communication node assigned to the management station in the asynchronous communication phase, a communication node assigned to an ordinary station, in the asynchronous communication phase, transmits object data by making a transmission request to obtain a transmission opportunity.
Japanese Patent Application Publication No. 2004-86367-A describes an apparatus for diagnosing plant network integrity. Controllers and an operator console are connected like a star through a repeater. The apparatus for diagnosing plant network integrity is configured to directly connect a data collection means to the repeater, and directly connect a check means to a data collection means. The data collection means receives and collects all the frames transmitted to a plant network. A fixed cyclic data check means of the check means checks a frame by comparing a frame transmitted in a fixed cycle with pre-recorded frame reference information. Thus the abnormality of the controller is determined.